Injection molded heat dissipation device

ABSTRACT

Heat dissipation devices and molding processes for fabricating such devices, which have at least two regions comprising different conductive materials such that efficient thermal contact is made between the different conductive materials. The molding processes include injection molding at least two differing conductive materials.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to heat dissipation devices andmethods for fabricating the same. In particular, the present inventionrelates to a multiple step injection molding technique used to form aheat dissipation device comprising at least two separate conductivematerial regions.

[0003] 2. State of the Art

[0004] Higher performance, lower cost, increased miniaturization ofintegrated circuit components, and greater packaging density ofintegrated circuits are ongoing goals of the computer industry. As thesegoals are achieved, microelectronic dice become smaller. Accordingly,the density of power consumption of the integrated circuit components inthe microelectronic die has increased, which, in turn, increases theaverage junction temperature of the microelectronic die. If thetemperature of the microelectronic die becomes too high, the integratedcircuits of the microelectronic die may be damaged or destroyed.

[0005] Various apparatus and techniques have been used and are presentlybeing used for removing heat from microelectronic dice. One such heatdissipation technique involves the attachment of a high surface areaheat sink to a microelectronic die. FIG. 12 illustrates an assembly 300comprising a microelectronic die 302 (illustrated as a flip chip)physically and electrically attached to a substrate carrier 304 by aplurality of solder balls 306. A heat sink 308 is attached to a backsurface 312 of the microelectronic die 302 by a thermally conductiveadhesive 314. The heat generated by the microelectronic die 302 is drawninto the heat sink 308 (following the path of least thermal resistance)by conductive heat transfer.

[0006] High surface area heat sinks 308 are generally used because therate at which heat is dissipated from a heat sink is substantiallyproportional to the surface area of the heat sink. The high surface areaheat sink 308 usually includes a plurality of projections 316 extendingsubstantially perpendicularly from the microelectronic die 302. It is,of course, understood that the projections 316 may include, but are notlimited to, elongate planar fin-like structures and columnar/pillarstructures. The high surface area of the projections 316 allows heat tobe convectively dissipated from the projections 316 into the airsurrounding the high surface area heat sink 308. A fan 318 may beincorporated into the assembly 300 to enhance the convective heatdissipation.

[0007] The heat sinks 308 may be fabricated by molding, such asinjection or extrusion, or by forming the projections 316 from a blockof conductive material (such as by skiving) or attaching projections(such as folded fins) to a conductive block. Furthermore, the heat sinks308 may be constructed from a thermally conductive material, such ascopper, silver, gold, aluminum, and alloys thereof. However, althoughcopper, gold, and silver have excellent thermal conductivity (e.g.,greater than about 300 J/(s*m*°C.) between about 0° C. and 100° C.),they are heavy (e.g., specific gravities of greater than about 8.0),such that the weight of the heat sink 308 could damage themicroelectronic die 302 to which it is attached. Furthermore, they areexpensive (prohibitively so with gold and silver) relative to otherconductive materials. Thus, less expensive and lighter materials such asaluminum (i.e., a specific gravity of about 2.7) could be used. However,since aluminum and other lighter materials generally have lower thermalconductive properties lower than gold, silver, and copper (less thanabout 300 J/(s*m*°C.) between about 0° C. and 100° C.), they may nothave sufficient thermal conductive properties to adequately cool a highheat producing microelectronic die 302.

[0008] Thus, some heat sinks are a combination of highly thermallyconductive materials and lightweight, relatively, less thermallyconductive material to form multiple conductive material designs. FIG.13 illustrates such a heat sink 320 comprising a highly thermallyconductive plate portion 322 (such as copper) and a lightweightthermally conductive, high surface area portion 324 (such as aluminum)having projections 326 thereon. The plate portion 322 and the highsurface area portion 324 are attached to one another by any knownconnection method. This design allows the highly thermally conductiveplate portion 322 to thermally contact the microelectronic die 302 foreffective heat removal and to conduct the heat to the lighter, highsurface area portion 324 for convective dissipation to the surroundingair.

[0009] Another design of a heat sink 330 comprises an extruded,lightweight, high surface area portion 332 having a plurality ofprojections 334 and a highly conductive plate portion 336 which has beenpressed into the high surface area portion 332, as shown in FIG. 14.Both multiple metal designs of FIGS. 13 and 14 result in lightweightheat sinks; however, the interface between the high surface areaportions and the plate portions may not have an efficient contact.Surface variations between the high surface area portion and the plateportion may result in very small voids/air spaces, which reduces theefficiency of the thermal contact therebetween.

[0010] Therefore, it would be advantageous to develop techniques tofabricate a multiple material heat sink that has efficient thermalcontact between the various materials in the heat sink.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] While the specification concludes with claims particularlypointing out and distinctly claiming that which is regarded as thepresent invention, the advantages of this invention can be more readilyascertained from the following description of the invention when read inconjunction with the accompanying drawings to which:

[0012]FIG. 1 is a side cross-sectional view of a first embodiment of aheat dissipation device attached to a microelectronic die, according tothe present invention;

[0013]FIG. 2 is a side cross-sectional view of a mold core with a firstmold having a cavity defined therein abutted against the mold core,according to the present invention;

[0014]FIG. 3 is a side cross-sectional view of a first conductivematerial injected into the first mold cavity of FIG. 2, according to thepresent invention;

[0015]FIG. 4 is a side cross-sectional view of the first mold of FIG. 3removed from the mold core, according to the present invention;

[0016]FIG. 5 is a side cross-sectional view of a second mold having acavity defined therein abutted against the mold core as shown in FIG. 4,according to the present invention;

[0017]FIG. 6 is a side cross-sectional view of a second conductivematerial injected into the second mold cavity of FIG. 5, according tothe present invention;

[0018]FIG. 7 is a side cross-sectional view of the second mold of FIG. 6removed from the mold core, according to the present invention;

[0019]FIG. 8 is a side cross-sectional view of a mold core with a moldhaving a cavity defined therein abutted against the mold core, accordingto the present invention;

[0020]FIG. 9 is a side cross-sectional view of a first conductivematerial injected into and partially filling the mold cavity of FIG. 8,according to the present invention;

[0021]FIG. 10 is a side cross-sectional view of a second conductivematerial injected into the mold cavity of FIG. 9, according to thepresent invention;

[0022]FIG. 11 is a side cross-sectional view of the second mold of FIG.10 removed from the mold core, according to the present invention;

[0023]FIG. 12 is a side cross-sectional view of a heat dissipationdevice attached to a microelectronic die, as known in the art; and

[0024]FIGS. 13 and 14 are side cross-sectional views of multiplematerial heat dissipation devices attached to microelectronic dice, asknown in the art.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

[0025] In the following detailed description, reference is made to theaccompanying drawings that show, by way of illustration, specificembodiments in which the invention may be practiced. These embodimentsare described in sufficient detail to enable those skilled in the art topractice the invention. In addition, it is to be understood that thelocation or arrangement of individual elements within each disclosedembodiment may be modified without departing from the spirit and scopeof the invention. The following detailed description is, therefore, notto be taken in a limiting sense, and the scope of the present inventionis defined only by the appended claims, appropriately interpreted, alongwith the full range of equivalents to which the claims are entitled. Inthe drawings, like numerals refer to the same or similar functionalitythroughout the several views.

[0026] The present invention relates to a process for fabricating a heatdissipation device, which has at least two regions comprising differentconductive materials wherein an efficient thermal contact is madebetween the different conductive materials. Broadly, the presentinvention relates to a molding process, such a two-shot molding processknown in the plastics industry, wherein the heat dissipation device ismolded with at least two injections of differing thermally conductivematerials.

[0027]FIG. 1 illustrates a microelectronic assembly 100 of the presentinvention comprising a heat dissipation device 102 attached to amicroelectronic die 104 (illustrated as a flip chip). Themicroelectronic die 104 is physically and electrically attached to asubstrate 106 by a plurality of solder balls 108. The heat dissipationdevice 102 comprises a highly thermally conductive portion 112 (e.g.,thermal conductivity higher than about 300 J/(s*m*°C.) between about 0°C. and 100° C.), such as copper (e.g., approximate thermal conductivityof 397 J/(s*m*°C.) between about 0° C. and 100° C.) and a secondthermally conductive portion, shown as finned portion 114 having aplurality of projections 116, comprising a lightweight weight conductivematerial, such as aluminum (e.g., approximate thermal conductivity of238 J/(s*m*°C.) between about 0° C. and 100° C.). The heat dissipationdevice 102 further includes a molded interface 120 between the highlythermally conductive portion 112 and the second thermally conductiveportion (shown as finned portion 114).

[0028] It is, of course, understood that the projections 116 mayinclude, but are not limited to, elongate planar fin-like structures(extending perpendicular to the figure) and columnar/pillar structures.Preferably, the projections 116 extend substantially perpendicularly toa substantially planar mounting surface 118 of the heat dissipationdevice 102.

[0029] As shown in FIG. 1, the heat dissipation device mounting surface118 is attached to a back surface 122 of the microelectronic die 102,preferably by a thermally conductive adhesive 124. Although the heatdissipation device 102 is illustrated as being attached to themicroelectronic die 104, the invention is, of course, not so limited.The heat dissipation device 102 may be attached to any surface fromwhich heat is desired to be dissipated. Preferably, the highly thermallyconductive portion 112 resides adjacent the heat source. It is alsopreferred that the highly thermally conductive portion 112 comprises aportion of said heat dissipation device mounting surface 118.

[0030] FIGS. 2-7 illustrate one embodiment of a method of fabricating aheat dissipation device. As shown in FIG. 2, a first mold 132 having acontact surface 136 and a cavity 134 defined therein is provided. Thefirst mold contact surface 136 is placed against a contact surface 138of a mold core 142. The mold core 142 has at least one first “channel”or “gate” 144 extending through the mold core 142, wherein the firstgate 144 has at least one opening (shown as a single opening 146) at themold core contact surface 138. The first gate opening 146 is positionedat the first mold cavity 134 when the first mold 132 and the mold core142 are placed together. It is noted that the mold core 142, as shown,has at least one second gate (shown as two second gates 148 and 148′)which will be utilized in subsequent steps, but whose opening(s) (shownas openings 152 and 152′, respectively) are presently blocked by thefirst mold contact surface 136.

[0031] As shown in FIG. 3, a high thermal conductivity material 154 isinjected through the first gate 144 to fill the first mold cavity 134(vent holes for the first mold cavity 134 are not shown). The first mold132 is then removed thereby forming the highly thermally conductiveportion 156 (similar to element 112 of FIG. 1) of the heat dissipationdevice being fabricated, as shown in FIG. 4. Although the highlythermally conductive portion 156 is shown as being hemispherical, thefirst mold cavity 134 may be adapted to form the highly thermallyconductive portion 156 to any suitable shape.

[0032] As shown in FIG. 5, a second mold 162 is placed on the mold core142, wherein a contact surface 164 of the second mold 162 contacts themold core contact surface 138. The second mold 162 includes a cavity166, which is disposed to encompass the highly thermally conductiveportion 156 and allows access thereto by at least one second gateopening (shown as the openings 152 and 152′). The second mold cavity 166is preferably shaped with recesses 170 to form projections for the heatdissipation device being fabricated.

[0033] As shown in FIG. 6, a lightweight conductive material 168,preferably aluminum, is injected through the second gates 148 and 148′to fill the second mold cavity 166 (vent holes for the second moldcavity 166 are not shown) to abut the highly thermally conductiveportion 156, which forms a molded interface 160 therebetween, and toform a second thermally conductive portion, shown as a finned portion172 having a plurality of projections 174 (similar to elements 114 and116 of FIG. 1). As shown in FIG. 7, the combination of the highlythermally conductive portion 156 and the finned portion 114 form a heatdissipation device 176. The heat dissipation device 176 is removed fromthe mold core 142 and second mold 162, and may then be further processedand/or thermally attached to any surface from which heat is desired tobe dissipated.

[0034] The molded interface 160, between the highly thermally conductiveportion 156 and the second conductive portion (shown as finned portion172), formed by the molding procedure of the present inventionsubstantially eliminates surface variations therebetween, which resultsin an efficient thermal interface.

[0035] The high thermal conductivity material 154 and the lightweightconductive material 168 may each be injected while in a molten state or,preferably, injected in a powdered or particulate form with a carrier orbinder material, as known in the art. For example, fine metal particles,usually less than about 25 microns in average diameter, are hot mixedwith a plastic or polymeric binder, such as polyvinyl alcohol,polypropylene, polyethylene, and with like, with a plasticizer, ifnecessary. The mixture is then cooled and granulated to form afeedstock. The feedstock is preferably between about 70 and 95% powderedmetal by weight. The part is then molded, as discussed above. A majorityof the binder material is removed from the part by baking the part in anoven at an elevated temperature, dissolving the binder with a chemicalsolvent, or removing the binder with a catalyst (by catalytic reaction).The part may then be sintered wherein the part is brought within a fewdegrees of its melting point. With the two metal configuration in thepresent invention, it would be within a few degrees for the metal havingthe lowest melting point. Sintering densifies the part, which may shrinkthe size of the part. Thus, the molds may have to be made to a sizelarger than the actual size of the finished part to compensate for theshrinkage.

[0036] FIGS. 8-11 illustrate another embodiment of a method offabricating a heat dissipation device. As shown in FIG. 8, a mold 202having a contact surface 206 and a cavity 204 defined therein isprovided. The mold contact surface 206 is placed against a contactsurface 208 of a mold core 212. The mold core 212 has at least one first“channel” or “gate” 214 extending through the mold core 212, wherein themold core gate 214 has at least one opening (shown as a single opening216) at the mold core contact surface 218. The mold core opening 216 ispositioned at the mold cavity 204 when the mold 202 and the mold core212 are placed together. The mold cavity 204 is preferably shaped withrecesses 220 to form projections for the heat dissipation device beingfabricated.

[0037] As shown in FIG. 9, a lightweight conductive material 222,preferably aluminum, is injected through the mold core gate 214 to atleast partially fill the mold cavity 204 (vent holes for the mold cavity204 are not shown). As shown in FIG. 10, a high thermal conductivitymaterial 224 is injected through the mold core gate 214 to form a highlythermally conductive portion 226 (similar to element 112 of FIG. 1),which forms a molded interface 230 therebetween. The injection of thehigh thermal conductivity material 224 also pushes the lightweightconductive material 222 to fill the mold cavity 204 and form a secondthermally conductive portion (shown as finned portion 228 having aplurality of projections 232 (similar to elements 114 and 116 of FIG.1)). It is, of course, understood that the mold core 212 could havemultiple gates and that the lightweight conductive material 222 and thehigh thermal conductivity material 224 could be injected throughdifferent mold core gates.

[0038] As shown in FIG. 11, the combination of the highly thermallyconductive portion 226 and the finned portion 228 form a heatdissipation device 234. The heat dissipation device 234 is removed fromthe mold core 212 and mold 202, and may then be further processed and/orthermally attached to any surface from which heat is desired to bedissipated.

[0039] Having thus described in detail embodiments of the presentinvention, it is understood that the invention defined by the appendedclaims is not to be limited by particular details set forth in the abovedescription, as many apparent variations thereof are possible withoutdeparting from the spirit or scope thereof.

What is claimed is:
 1. A heat dissipation device, comprising: a firsthighly thermally conductive portion; and a second thermally conductiveportion abutting said first highly thermally conductive portion with amolded interface.
 2. The heat dissipation device of claim 1, whereinsaid first highly thermally conductive portion has a thermallyconductivity greater than a thermal conductivity of said secondthermally conductive portion.
 3. The heat dissipation device of claim 1,wherein said first highly thermally conductive portion comprises copper.4. The heat dissipation device of claim 1, wherein said second thermallyconductive portion comprises aluminum.
 5. The heat dissipation device ofclaim 1, wherein said second thermally conductive portion includes aplurality of projections.
 6. A microelectronic assembly, comprising: amicroelectronic die; a heat dissipation device abutting saidmicroelectronic die, wherein said heat dissipation device comprises: afirst highly thermally conductive portion; and a second thermallyconductive portion abutting said first highly thermally conductiveportion with a molded interface.
 7. The microelectronic assembly ofclaim 6, wherein said first highly thermally conductive portion has athermally conductivity greater than a thermal conductivity of saidsecond thermally conductive portion.
 8. The microelectronic assembly ofclaim 6, wherein said first highly thermally conductive portioncomprises copper.
 9. The microelectronic assembly of claim 6, whereinsaid second thermally conductive portion comprises aluminum.
 10. Themicroelectronic assembly of claim 6, wherein said second thermallyconductive portion includes a plurality of projections.
 11. Themicroelectronic assembly of claim 6, wherein said heat dissipationdevice further includes a mounting surface which abuts saidmicroelectronic die, wherein at least a portion of said mounting surfacecomprises said first highly thermally conductive portion.
 12. Themicroelectronic assembly of claim 11, wherein said portion of said firsthighly thermally conductive portion of said heat dissipation abuts saidmicroelectronic die.
 13. A method of fabricating a heat dissipationdevice, comprising: providing a first mold having a cavity definedtherein and having a contact surface; providing a mold core having acontact surface and at least one first gate extending therethrough, andat least one second gate extending therethrough, said mold core firstgate and said mold core second gate each having at least one opening atsaid mold core contact surface; abutting said first mold contact surfaceagainst said mold core contact surface such that said at least one moldcore first gate opening is position within said first mold cavity;injecting a high thermal conductivity material through said at least onemold core first gate to fill said first mold cavity to form a highlythermally conductive portion; removing said first mold; providing asecond mold having a cavity defined therein and having a contactsurface; abutting said second mold contact surface against said moldcore contact surface such that at least one mold core second gateopening is positioned within said second mold cavity, and such that saidsecond mold cavity encompasses at least a portion of said highlythermally conductive portion; injecting a thermal conductive materialthrough said at least one mold core second gate into said second moldcavity to form a second conductive portion; and removing said highlythermally conductive portion and said second conductive portion fromsaid second mold.
 14. The method of claim 13, wherein injecting saidhigh thermally conductivity material through said at least one mold corefirst gate comprises injecting a high thermal conductivity materialcomprising copper through said at least one mold core first gate. 15.The method of claim 14, wherein injecting said high thermallyconductivity material through said at least one mold core first gatecomprises injecting a high thermal conductivity material comprisingcopper and a carrier material through said at least one mold core firstgate.
 16. The method of claim 15, wherein injecting said high thermallyconductivity material through said at least one mold core first gatecomprises injecting a high thermal conductivity material comprisingcopper and a polymer carrier material through said at least one moldcore first gate.
 17. The method of claim 13, wherein injecting saidthermal conductive material through said at least one mold core secondgate comprises injecting a thermal conductive material comprisingaluminum through said at least one mold core second gate.
 18. The methodof claim 17, wherein injecting said thermal conductive material throughsaid at least one mold core second gate comprises injecting a thermalconductive material comprising aluminum and a carrier material throughsaid at least one mold core second gate.
 19. The method of claim 18,wherein injecting said thermal conductive material through said at leastone mold core second gate comprises injecting a thermal conductivitymaterial comprising aluminum and a polymer carrier material through saidat least one mold core second gate.
 20. The method of claim 13, whereinproviding said second mold having a cavity defined therein comprisesproviding said second mold having a cavity defined with recesses to forma plurality of projections.
 21. A method of fabricating a heatdissipation device, comprising: providing a mold having a cavity definedtherein and having a contact surface; providing a mold core having acontact surface and at least one gate extending therethrough, said atleast one mold core gate having at least one opening at said mold corecontact surface; abutting said mold contact surface against said moldcore contact surface such that at least one mold core gate opening isposition within said mold cavity; injecting a thermal conductivematerial through said at least one mold core gate into said mold cavity;injecting a high thermal conductivity material through said at least onemold core gate to form a highly thermally conductive portion; andremoving said highly thermally conductive portion and said secondconductive portion from said mold.
 22. The method of claim 21, whereininjecting said high thermal conductivity material through said at leastone mold core gate comprises injecting a high thermal conductivitymaterial comprising copper through said at least one mold core gate. 23.The method of claim 22, wherein injecting said high thermal conductivitymaterial through said at least one mold core first gate comprisesinjecting a high thermal conductivity material comprising copper and acarrier material through said at least one mold core first gate.
 24. Themethod of claim 23, wherein injecting said high thermal conductivitymaterial through said at least one mold core first gate comprisesinjecting a high thermal conductivity material comprising copper and apolymer carrier material through said at least one mold core first gate.25. The method of claim 21, wherein injecting said thermal conductivematerial through said at least one mold core gate comprises injecting athermal conductive material comprising aluminum through said at leastone mold core gate.
 26. The method of claim 25, wherein injecting saidthermal conductive material through said at least one mold core secondgate comprises injecting a thermal conductive material comprisingaluminum and a carrier material through said at least one mold coresecond gate.
 27. The method of claim 26, wherein injecting said thermalconductive material through said at least one mold core second gatecomprises injecting a thermal conductivity material comprising aluminumand a polymer carrier material through said at least one mold coresecond gate.
 28. The method of claim 21, wherein providing said moldhaving a cavity defined therein comprises providing said mold having acavity defined with recesses to form a plurality of projections.